Devices of the generic type described supra are known in the art. The devices are used for example for determining a concentration of oxygen in a gaseous volume flow. A typical application can be for example determining an oxygen concentration in air that is exhaled by a person in order to determine how much oxygen has to be added to the exhaled air so that the exhaled air is suitable for the person as fresh breathing air.
The sensor units of these devices are typically made from a luminescent chemical substance whose luminescence changes as a function of the concentration of the analyte. An excitation of the sensor unit with light causes a light radiation from the sensor unit, wherein properties of the radiation coming from the sensor unit allow a conclusion with respect to the concentration of the analyte in or at the sensor unit.
Various devices are known in the art which use this technology or a comparable technology for determining a concentration of an analyte in a media flow. Reference is made to the International patent applications WO 2005/100957 A1 and WO 2013/181679 A1 and German Patent Application DE 10 2014 112 972 A1.
A typical problem when determining a concentration of an analyte with an optical sensor unit is that this type of sensor unit has a very high sensitivity relative to changing temperatures. This sensitivity has the effect that luminescent properties of the sensor unit also change as a function of the temperature change. Therefore it is not possible to derive a direct conclusion from a change of the luminescence of the sensor unit with respect to the cause of the change so that in particular no direct conclusion regarding the concentration of the analyte in the medium to be analyzed is possible.
In order to deal with the problem temperature sensors are used in the art which continuously monitor the temperature of the sensor unit. Thus, it is particularly relevant that a change of the temperature of the sensor unit is detected rather quickly so that it can be considered when processing the radiation emitted by the sensor unit. In case there is a time lag between the change of the temperature of the sensor unit and its detection by a temperature measuring device initially a particular transition time has to be provided when the temperature of the sensor unit changes before a reliable statement regarding the concentration of the respectively analyzed analyte can be made. Furthermore it is relevant that the temperature of the sensor unit deviates as little as possible from the temperature that is detected by the temperature measuring device. Deviations can be introduced by different temperatures of the medium to be examined and the housing. These deviations can have a negative influence upon the precision of the measurement of the analyte.
In order to keep the described time lag and temperature differences at a minimum it is proposed in the art for example to bring a temperature measuring device in direct contact with the respective sensor unit and to detect a temperature change of the sensor unit with the smallest delay possible. This method, however, has the problem that the respective temperature measuring device has to be run out of the electronics housing of the device and is therefore in direct contact with the respective medium to be analyzed like the sensor unit. In particular, there is a risk that an unintentional passage of the medium to be analyzed occurs through the opening of the housing into the housing wherein the opening is provided for the temperature measuring device so that the electronics are damaged.